"initialize" class method for classes in Swift?

There is no type initializer in Swift.

“Unlike stored instance properties, you must always give stored type properties a default value. This is because the type itself does not have an initializer that can assign a value to a stored type property at initialization time.”

Excerpt From: Apple Inc. “The Swift Programming Language.” iBooks.

---

You could use a type property which default value is a closure. So the code in the closure would be executed when the type property (or class variable) is set.

class FirstClass {
    class var someProperty = {
     // you can init the class member with anything you like or perform any code
        return SomeType
    }()
}

But class stored properties not yet supported (tested in Xcode 8).

One answer is to use static, it is the same as class final.

Good link for that is

Setting a Default Property Value with a Closure or Function

Excerpt From: Apple Inc. “The Swift Programming Language.” iBooks.

---

Code example:

class FirstClass {
    static let someProperty = {
        () -> [Bool] in
        var temporaryBoard = [Bool]()
        var isBlack = false
        for i in 1...8 {
            for j in 1...8 {
                temporaryBoard.append(isBlack)
                isBlack = !isBlack
            }
            isBlack = !isBlack
        }

        print("setting default property value with a closure")
        return temporaryBoard
    }()
}

print("start")
FirstClass.someProperty

Prints

start

setting default property value with a closure

So it is lazy evaluated.

For @objc classes, class func initialize() definitely works, since +initialize is implemented by the Objective-C runtime. But for "native" Swift classes, you'll have to see the other answers.

If you have an Objective-C class, it's easiest to just override +initialize. However, make sure subclasses of your class also override +initialize or else your class's +initialize may get called more than once! If you want, you can use dispatch_once() (mentioned below) to safeguard against multiple calls.

class MyView : UIView {
  override class func initialize () {
    // Do stuff
  }
}

 

If you have a Swift class, the best you can get is dispatch_once() inside the init() statement.

private var once = dispatch_once_t()

class MyObject {
  init () {
    dispatch_once(&once) {
      // Do stuff
    }
  }
}

This solution differs from +initialize (which is called the first time an Objective-C class is messaged) and thus isn't a true answer to the question. But it works good enough, IMO.